Editor's note: This is the first in a three-part series. Coming next, why the Mount Polley disaster could repeated in the transboundary region of British Columbia and Southeast Alaska. The second installment is available here.

One of the most frequent claims of promoters of the proposed Pebble Mine at the headwaters of Bristol Bay, Alaska, is that modern technology means the failures of “tailings ponds” is highly unlikely. However, just this week, an earthen dam at the Mount Polley Copper mine in British Columbia, Canada, failed, releasing an estimated 1.3 billion gallons of contaminated tailings into the Fraser River watershed, known for its abundance of sockeye salmon. What we’ve seen this week is exactly why TU is supporting the Environmental Protection Agency (EPA) effort to limit mining activities in Bristol Bay.

When the EPA assessed the potential impacts of large scale mining in the area, the Pebble Limited Partnership, which owns the claim to the Pebble deposit, hired an engineering firm to critique the EPA’s findings. The consultants said [PDF], “Modern dam design technologies are based on proven scientific/engineering principles and there is no basis for asserting that they will not stand the test of time.”

There’s just one problem: the consulting firm PLP hired, Knight Piesold Limited, engineered the tailing dam at Mt. Polley. Worse yet, PLP also hired them to design their tailings dam at the Pebble deposit.You read that right. The same company that PLP hired to criticize the EPA’s assessment, who argued there is no reason to believe these dams will fail, engineered a dam that failed, and is on the hook for building a similar structure at the headwaters of one of the best salmon fisheries in the world.

The impact in the Fraser watershed has been disastrous. Waters are off limits to swimming, and drinking. Dr. Peter Ross of the Vancouver Aquarium says the failure means, “sudden, lethal injury to fish and their feed." Over the long run, sediment loads will bury salmon spawning sites, and deposit toxic chemicals into the streambed. That’s a serious problem for the estimated 1.5 million sockeye salmon which return to waters near the mine every year. You can see a short video of the damage below: